Method of making shaft seal with clinch-butt metal case

ABSTRACT

An elastomeric radial lip shaft seal and method of making same wherein the seal is provided with a rigid reinforcing member of generally cylindrical shape and formed from strip stock with the ends thereof joined by clinch-butt construction.

This is a division of application Ser. No. 673,577 filed Apr. 5, 1976and now U.S. Pat. No. 4,052,077.

BACKGROUND OF THE INVENTION

This invention relates to a conventional radial type shaft seal with anelastomeric body which is supported by a rigid metallic case.

The metal case is a necessary part of the seal in that it stabilizes thediameter of the seal through repeated changes in operationaltemperature. Without the metal case, the elastomer, having a differentcoefficient of thermal expansion from the bore in which it fits, becomesloose and the assembly fails with repeated temperature cycling.

Heretofore the metal case has been one of the most expensive parts of aconventional shaft seal because of the large amount of waste materialinvolved in the manufacture of this component. Present state of the arthas been to form this part from a flat ring or washer which when upsetby cold forming becomes generally cylindrical. Traditionally, however,the basic flat ring is cut from rectangular or strip sheet-stock so thatgeometrically speaking the outsides between the rings becomes scrap aswell as the insides which must be removed by a piercing operation.

The present invention relates to the fabrication of the generallycylindrical metal cases from small rectangular blanks of sheet stockthat in turn can be cut from large rectangular or strip stock with verylittle waste. The small rectangular blanks, then, are formed so that thenarrow ends can be fastened together to produce the desired generallycylindrical seal cases. When this is done, the flat ring phase thatproduces the scrap in the present state of the art is deleted from themanufacturing process and scrap production is reduced from approximately30% to less than 5% of the original sheet stock. Such a saving wouldallow four seals to be made from a piece of metal that formerly producedonly three seals.

SUMMARY OF THE INVENTION

The present invention incorporates a formed split or drawn type metalliccase to maintain diametrical stability of a radial shaft seal. The casepreferably includes a radial flange having an annularly inward extendingterminal portion or flange to which is bonded the elastomeric seal body.The butt joint can be made by any fastening method that maintainsstability of the case such as spring tension, clinch-butt, welding, oradhesive. Our primary intent, however, is to use generally rectangularshaped pieces of sheet metal with which to form the seal case. The basicrectangular shape is required because it is the only geometric shapefrom which a generally cylindrical ring can be formed that can be cutfrom strip stock with no waste between the primary cuts.

Secondary cuts may be made to facilitate subsequent forming operationsbut it has been determined that these cuts produce substantially lesswaste material than do the same size rings cut directly from rectangularsheet stock.

Other objects and advantages of the invention will appear from thefollowing description of a preferred embodiment.

BRIEF DESCRIPTION OF DRAWINGS

In the drawings:

FIG. 1 is an isometric drawing of a complete seal embodying theprinciples of the invention with an internal flange on a clinch-butttype case.

FIG. 2 is a cross-section along line 2--2 of FIG. 1.

FIG. 3A is a progressive representation of the case formation showingareas of waste production.

FIG. 3B is an isometric drawing of a finished case produced from theinvention.

FIG. 3C is a similar representation of conventional case formationshowing areas of waste production.

FIG. 4 is an end view of the second or "U" forming operation.

FIG. 5 is an end view of the third or finish ring forming operation.

FIGS. 6A thru 6E are views in cross-section and isometrics showing theprogressive formation of a radial flange on the generally cylindricalcase.

FIG. 7 is an exploded view in cross-section of the finished metal casein relation to the mold in which the elastomer is cured and bonded.

FIG. 8 is a view similar to FIG. 7 in which the mold is closed for cureand bonding of the elastomer to the metal case.

FIG. 9 is an isometric view of a completed seal with an external metalflange.

FIG. 10 is an end view of the seal in FIG. 9 showing elastomeric webbingor reinforcing ribs used for axial support of the sealing element.

FIG. 11 is a cross-section taken at line 11--11 in FIG. 10 showing theexternal metal flange and internal elastomeric reinforcing ribs.

DESCRIPTION OF A PREFERRED EMBODIMENT

FIGS. 1 and 2 show a finished radial lip type shaft seal wherein theouter case or metal reinforcing member 10, is generally made from sheetsteel. The case 10 is provided with a cylindrical portion having a boreengaging surface 18 and a radially extending flange 11. Case 10 isjoined at it's circumference by means of a clinch-butt joint 13. Thebutt joint 13 is held together by male protrusions or clinches 14 on oneside that fit into female locking devices or clinches 15 on the otherside. An elastomeric body 16 is molded and bonded, in a manner describedhereinbelow, to axially inner surfaces 19 and 20 of portions 10 and 11,respectively.

The elastomer of the sealing element 12 includes a bonded body portionwhich extends to cover the entire inside of the case 10 as seen in FIG.2 and extends further to cover both edges 17 of the case 10 to preventpossible leakage through the butt joint 13. Covering any three surfaces(inside, outside, two edges) will prevent leakage through the joint. Theelastomeric body has a main body portion bonded to on the axially innersurfaces 19 and 20, and beyond it is a main lip portion 12 having a seallip 21 and a spring receiving groove 22 to receive, after molding, agarter spring.

With the exception of the clinch-butt joint 13 and that portion of theelastomeric body 16 which includes bonded body portions along innersurfaces 19 and 20, the seal structure depicted in FIGS. 1 and 2 isconventional. These differences in structure are largely due to ournovel method of manufacturing radial type shaft seals. As seen in FIG.3A, our preferred method of manufacture is to first form the cylindricalmetal case by feeding, from left to right, a strip of sheet stock 23into a progressive, cross-blank type die or stamping press.

FIG. 3A shows a typical sequence of operations performed by aprogressive die in the present invention for the production of afinished case 10 in FIG. 3B from a strip of sheet stock 23. An initialscoring operation 24 at the first station of a progressive die uses ablade above and a blade below the strip stock which when the die isclosed do not actually meet but come so close to each other that thestrip stock is partially cut or scored to the extent that the stock isstrong enough to move to successive positions but weak enough to tearprecisely when subjected to a slight shearing stress. Starting with thescore 24 as the first station, the second or trim station of theprogressive die shown at the left of FIG. 3A, trims to length or cutsthe male clinches 14 and the female clinches 15 with their half trianglenotches to develop the required length by shearing action. The smallbits of metal that are sheared off at the clinches and half trianglenotches if used are waste and are characteristic of the operation whencross-blanking is used as shown. If, however, the progressive die is setup for in-line operation, the male cuts of each piece becomes the femalecut for the successive piece and even more waste is eliminated.

The third or piercing operation of the progressive die produces morewaste only when triangular notches 25 are cut to allow the formation ofan internal flange 11. These notches are a device used to decrease theamount of material available and required to produce an internal radialflange with its characteristically decreasing rate of volume change asit approaches the center. Without the notches 25, the internal flange 11would become wrinkled in its formation when too much material would beforced into a cavity of two little volume.

In the fourth position or first forming operation 28, score 24 ispartially separated at 27 and the major axis of the generallyrectangular blank is bent to form a curve. At the fifth station thecurve is bent further to form a "U". At the sixth station the male andfemale clinch parts are coined and locked together, the ring is formedand severed entirely from the strip stock 23. In FIG. 3B the notched endis upset to form the internal flange 11 on the completed case 10.

FIG. 3C shows the prior art for a comparable seal case fabrication inwhich a hole 31 is punched in a piece of strip stock 32 leaving a slugas waste. More waste 34 is produced when a ring 35 is formed around thehole 31 and separated from the strip stock 32 to form a generallycylindrical case 10 with an internal flange 11.

A comparative study of these two methods of seal case manufacture showsthat the preferred method of the present invention depicted in FIG. 3Acan utilize 95% of the basic metal stock to produce seal cases whileonly 5% of the basic stock is wasted. In the prior art method of sealcase manufacture depicted in FIG. 3C an average of 70% of the basicstock can be made into seal cases while 30% of the basic stock iswasted. The 25% reduction of waste by the present invention over theprior art means that four seal cases can now be produced from the samestrip of metal that produced three seal cases by the prior art. Whenplain cylindrical cases without flanges can be used, production of wastecan be virtually eliminated.

FIG. 4 is an exploded end view of station 5 of FIG. 3A in which a formdie 36 continues the ring forming process by pressing the flat cut sheetmetal of station 4 in FIG. 3A over a mandrel 37 to produce a generallyU-shaped piece 38. This U-shaped piece 38 is then moved to station 6 ofFIG. 3A which is shown as an exploded end view in FIG. 5. At thisstation an upper forming die 39 and a lower form die 40 close on theU-shaped piece 38 of FIG. 4 to form a ring 41 around a mandrel 42. It isat this final station that the clinch-butt joint is assembled. Themating process between parts 14 and 15 of FIG. 3A is accomplished bycoining which is necessary because the parts 14 and 15 are designed withan interference fit. The extreme pressures, however, that are generatedwhen final forming dies 39 and 40 of FIG. 5 close around the mandrel 42cause the metal 41 to be coined or flow into available spaces to form asemi-permanent joint. In case a more permanent joint is required, thebond at the butt joint could be accomplished by brazing, soldering,welding, or any of several adhesives. The limitation for such a processwould be that the cost of the joint must be less than the cost of thescrap being saved. Other less critical applications might be adequatelyserved by a simple ring with no flange and no joint. Such an applicationcould be designed in which no waste would be produced.

FIGS. 6A thru 6E show the formation of an internal flange on the ring 41shown in FIG. 5. The first stage of this process shows a cross-sectionof the first form die 43 partially closed around a ring 41 which hasbeen inserted over a form punch 44. Closing this die completely willupset ring 41 so that the flange area 45 is about half formed as shownon ring 47. The next phase takes ring 47 and places it on the final formpunch 46 which is shown in cross-secton with the internal flange 48completely formed and shown in perspective as part of a finished ring49.

FIG. 7 is an exploded view of a partial cross-section of a typicalradial shaft seal molding operation in which the ring 65 of the presentinvention is shown in relation to the other molding components. Thetaper 51 of the lower cavity 52 fits the taper 53 of the center ring 54.The ring 65 of the present invention is a press fit into the center ring54 at the interface 55. The external taper 56 of the upper cavity 57fits into the taper 58 of the center ring 54 while the internal taper 59of the upper cavity fits into the top taper 60 of the lower cavity 52 asthe mold is closed as shown in the partial cross-section of FIG. 8. Theelastomeric prep 61 of FIG. 7 is a ring of appropriate diameter ofuncured stock the volume of which is slightly larger than the volume ofthe cavity of the mold when it is in the closed position shown in FIG.8. Closing the mold, therefore, pressurizes the elastomeric prep 61 ofFIG. 7 and causes it to flow throughout the cavity 62 of the closed moldFIG. 8. Excess prep flows through a narrow channel 63 into a rind cavity64 where it remains while the elastomer is being cured by hightemperature and high pressure for a prescribed length of time. Aftercure the mold is opened, the seal is removed and the rind from cavity 64is easily torn away at the point where the narrow channel 63 leaves aweak area in the cured elastomer.

FIG. 9 is a side view in perspective of a radial lip shaft seal 70 ofthe present invention with an external flange 71. The end view from theoil or inside of this seal 70 is presented in FIG. 10 with slits 72opening up in the external flange 71 as the metal is stretched from itsinitial ring diameter 73 to the increased diameter 74 of the externalflange 71. Elastomer 75 is bonded to the inside of the initial ring 73to form the sealing element 76. The method of making metal case isidentical to that shown in FIGS. 3A to 6 with the exception of thestamping (scoring) of slits 72 in lieu of triangular notches 25, and thedie for forming flange 71 outwardly of case cylindrical portion 70. Itmay also be desirable for certain particular seal applications toeliminate the flange entirely and simply bond elastomeric body 75 solelyto the radially inner surface 78 of the cylindrical case portion.

Where the radially inward flange 11 of FIG. 1 is eliminated from thecase 10 it is deemed desirable for certain applications to makeintermediate portion of the elastomeric body 75 greater axially incross-sectional thickness than otherwise conventional for reinforcementor stability purposes as shown in FIG. 11. It may also be desirable toprovide this intermediate portion 75 with a series of reinforcing ribs77, formed by axially thickening the elastomeric body in selected placesas shown in FIGS. 10 and 11. Such design has the advantage of keepingthe amount of elastomeric material needed to a minimum and this feature,coupled with the reduction in strip material, produces a very economicalseal element.

To those skilled in the art to which this invention relates, manychanges in construction and widely differing embodiments andapplications of the invention will suggest themselves without departingfrom the spirit and scope of the invention. The disclosures and thedescription herein are purely illustrative and are not intended to be inany sense limiting.

We claim:
 1. A method for making radial lip shaft seals having agenerally cylindrical reinforcing outer case to which has been bonded anelastomeric body that includes a flexible seal lip portion comprisingthe steps of, selecting a rigid strip of indeterminate length, feedingsaid strip continuously through a series of punch press formingoperations in a progressive type die to perform the steps of: scoringthe strip rearwards of the body edge to establish the width of arectangular case blank at a first station, the first advance of saidcase blank to a second die station and trim step establishing the lengthof said rectangular case blank, a second advance of said rectangularcase blank to a third die station where the first form operation startsthe bending of said case blank along its major axis with some separationof said score at both edges,advancing said case blank to a fourth diestation with the second form operation increasing the bend of theprevious operation forming a "U" and greatly increasing the separationalong the score from the edges toward the middle, advancing said caseblank to a fifth die station with the third forming operation closingthe "U" of the previous operation and forming the generally cylindricalshape of a finished reinforcing outer case, placing said finished casein the heated cavity of a mold in a molding press with a quantity ofuncured elastomer and bonding said elastomer to said finished caseforming said elastomeric body and said flexible lip seal portion.
 2. Themethod of making radial lip shaft seals in claim 1 where said rigidstrip of indeterminate length is sheet metal.
 3. The method of makingradial lip shaft seals in claim 1 in which the second progressive diestation has been modified forming at least one male clinch at one end ofsaid rectangular case blank and at least one corresponding female clinchat the other end of said rectangular case blank said male and femaleclinches being coined together at the fifth progressive die station. 4.The method of making radial lip shaft seals in claim 1 in which thesecond progressive die station has been modified to form half trianglenotches at the ends of said rectangular case blank with bases extendingalong said score and an extra piercing station added between said secondtrim station and said third or form station to form at least twotriangular cut-out portions the bases of which extend along said scoreintermediate and substantially equally spaced between the said halftriangle notches and after said complete separation at said score,shaping said case blank over a preform punch by a preform die displacingthe segments between the triangular notches of said case blank radiallyinward to an angle of approximately 45° with the axis of said case blankand shaping over a finish form punch by a finish form die increasing thedisplacement of said segments to an angle of approximately 90° with theaxis forming an internal flange of a finished case.
 5. The method ofmaking radial lip shaft seals of claim 4 in which slits of length equalto the height of said triangles and replacing said triangles so thatpreform and finish form operations produce displacements radiallyoutward of the formed segments resulting in external flanges on thefinished cases.